Recently, the so-called multimedia trend in the electric household appliances and computer apparatus has been promoted, and devices for transmitting and receiving image data have come to be used widely.
A conventional communication apparatus is described below. FIG. 12 and FIG. 13 show a constitution of a conventional communication apparatus.
Reference numeral 101 denotes an image memory, in which image data is developed as bit map data and recorded. Reference numeral 102 denotes a display circuit, which reads out the bit map data on the image memory 101, and converts and issues as display RGB signal. Reference numeral 103 is a microcomputer, which reads out bit map data, and converts into a fax format. Reference numeral 104 denotes a fax modem, which receives fax digital data converted by the microcomputer 103, modulates into an analog signal to be transmitted through a telephone circuit, and transmits to the telephone circuit through an NCU circuit 105. Reference numeral 106 denotes a fax apparatus, which is directly connected to the telephone circuit, and is used only for transmission and reception through the telephone circuit.
Referring to FIG. 13, the control actin of the NCU circuit 105 in FIG. 12 is described below. Reference numeral 111 is a fax modem, which is controlled by a microcomputer 112.
When the fax modem 111 transmits fax data to the telephone circuit, the microcomputer 112 confirms that a fax apparatus 114 is not in off-hook state by an off-hook detecting circuit 115 connected to the fax apparatus 114, and changes over a changeover circuit 110 to the fax modem side by the control of the microcomputer 112, sets an off-hook switch 113 connected to the fax modem 111 to an off-hook state, and then controls to transmit data to the telephone circuit.
When receiving fax data from the telephone circuit, on the other hand, a transmitted call signal is detected by a ring detecting circuit 116 connected to the telephone circuit, and when the fax apparatus 114 is not in off-hook state, the changeover circuit 110 is changed over to the fax modem side by the control of the microcomputer 112, and the fax modem 111 hooks off the off-hook switch 113 by the control of the microcomputer 112. At this time, by a current source 117, a DC loop is formed in the telephone circuit, and an off-hook state is set up. Then the fax modem 111 receives the fax data.
The fax apparatus 114 is connected to the telephone circuit through a changeover circuit 110, and to transmit and receive a call signal with the telephone circuit, only after the changeover circuit 110 is changed over to the fax apparatus 114 side by the control by the microcomputer, transmission or reception of fax data with the telephone circuit is realized. However, since the fax modem 111 and fax apparatus 114 cannot be connected by the changeover circuit 110, transmission and reception between the fax modem 111 and fax apparatus 114 are disabled. Although not shown in the diagram, if the fax apparatus 114 is directly connected to the fax modem 111 without connecting through the telephone circuit, the fax modem 111 has no transmitting and receiving means of call signal with the fax apparatus 114 without communicating through the circuit, and therefore fax data cannot be transmitted or received automatically by the control of the microcomputer 112 between the fax modem 111 and fax apparatus 114.
In FIG. 13, incidentally, the bridge circuit and others necessary for the NCU circuit are omitted because they are not directly related to the description of the present invention.
Thus, in this constitution, the following problems are known.
(1) Since the NCU circuit 118 cannot send out a call signal to the fax apparatus 114 connected directly to the fax modem 111 without connecting through the telephone circuit, the fax apparatus 114 cannot control the NCU circuit 118 to hook off by receiving the call signal. As a result, data cannot be transmitted to the fax apparatus 114 connected directly without connecting through the telephone circuit.
(2) Since the NCU circuit 118 has no means for selecting the destination of transmission data whether the telephone circuit 119 or fax apparatus 114, the user cannot select the destination of the transmission data.
(3) Since the fax modem 111 cannot detect the call signal from the fax apparatus 114 connected directly to the fax modem 111 without connecting through the telephone circuit, the microcomputer 112 cannot control the fax apparatus 114 to hook off. As a result, data cannot be received from the fax apparatus 114 connected directly without connecting through the telephone circuit.
(4) Since the NCU circuit has no function for selecting the sender of reception data whether the telephone circuit 119 or fax apparatus 114, the user cannot select the sender of the reception data.